I don't know whether this might be a possibility. A couple of years ago, I was manoeuvering the van on some sloping ground and had the front very low where the van had been levelled. As the van turned, the jockey wheel swung and got stuck against the metal 'triangle' that points down from the draw bar. In this instance, it tore the tyre off the solid centre of the jockey wheel. I suppose something similar could have happened to yours? The only reason I noticed it at the time was that on soft ground, it took quite a divot...